Hematopoietic cells have very important roles in a number of different processes in the body. For example, leukocytic hematopoietic cells are important in maintaining the body""s defenses against disease; monocytes, macrophages and lymphocytes are involved in potentiating the body""s responses to infection and tumors, while granulocytes are involved in overcoming infection, parasites and tumors. Platelets, another hematopoietic cell, form an important element in the hemostatic mechanism through initiating thrombus formation by their adhesion to each other and to damaged surfaces, and by the release to factors which assist in the formation of the fibrin clot. Erythrocytes are mainly involved in the transport of oxygen.
All of these blood cells are derived from a single progenitor cell called the hematopoietic stem cell. Stem cells are both pluripotent, in that they give rise to all different cell types, and capable of self renewal. Hematopoietic stem cells make up only a small percentage of bone marrow cells and are normally quiescent. However, when stimulated to divide, these stem cells produce a differentiated daughter cell with great proliferative potential. Sequential rounds of division and differentiation give rise to an enormous amplification of cell numbers which is necessary for the production of mature blood cells. This process of division and differentiation is subject to regulation at many levels to control cell production.
Numerous studies have led to the definition of functions of several hematopoietic regulatory messengers. These biomolecules have been characterized as stimulatory, e.g., Colony Stimulating Factors (CSFs) and interleukins (IL-1, IL-3, IL-5 and IL-9); inhibitory, e.g., transforming growth factor-xcex2, (TGF-xcex2), interferon, prostaglandin E, tumor necrosis factor, macrophage inflammatory protein-1 (MIP-1), lactoferrin, acidic isoferritins, AcSKDP, and pEEDCK (a synthetic HP5B monomer); or enhancing, e.g., TGF-xcex2, IL-6, IL-4, IL-9, IL-11, MIP-1, MIP-2, leukemia inhibitory factor and Steel factor. Pelus et al. Experimental Hematology 1994, 22:239-247. Stimulatory biomolecules have been found to promote division of particular cell lineages. For examine, G-CSF derives neutrophil production, while erythropoietin promotes formation of erythrocytes.
A number of these biomolecules and additional agents have been found to induce the mobilization of hematopoietic stem cells.
A single injection of IL-8 has been shown to induce mobilization of pluripotent stem cells that are able to provide permanent reconstitution of myeloid cells and of T and B lymphocytes. Later-veer et al. Blood 1995, 85(8):2269-2275. IL-8 belongs to a family of pro-inflammatory molecules called chemokines. This family has been divided into two subfamilies, the CXC and CC chemokines, based on whether the first two cysteine residues in a conserved motif are adjacent to each other or are separated by an intervening residue. In general, CXC, which include IL-8, melanoma growth-stimulating activity (MGSA) and platelet factor 4 (PF4), are potent chemoattractants and activators of neutrophils but not monocytes. In contrast, CC chemokines, which include RANTES, monocyte chemotactic protein 1 (MCP-1) and MIP-1, are chemoattractants for monocytes but not neutrophils.
Stem cell inhibitors (SCIs) such as the CC chemokines, murine and human MIP-1xcex1 (LD78), have also been shown to enhance the release and mobilization of cells into the peripheral blood. WO 94/28916; Simm et al. Blood 1994, 84:2937.
Increased mobilization of stem cells in patients treated with sequentially administered interleukin-3 and GM-CSF compared with GM-CSF alone has been reported by Brugger et al. Blood 1992, 79:1193-1200. In addition, it has been shown that the absolute number of peripheral blood progenitor cells can be expanded in vitro by culture in a cocktail of cytokines, usually including SCF, IL-3, and either IL-6 or IL-1. Bodine, D. Experimental Hematology 1995, 23:293-295.
SKandF 107647, a hematoregulatory agent containing an ethylene bridge in place of the cysteine bridge of HP5B, has been demonstrated to be a potent stimulator of in vitro myelopoiesis. Pelus et al. Experimental Hematology 1994, 22:239-247. Injection of SKandF 107647 in normal mice resulted in a two- to six-fold increase in serum colony-stimulating activity. Administration of this agent over 4 days resulted in significant increases in the number of granulocyte-macrophage, erythroid, and multipotential progenitor cells, as well as stimulating their cell cycle rates.
It has also been found that pretreatment with stem cell stimulating factor such as G-CSF can expand the pool of progenitor cells susceptible for mobilization by these agents, further increasing their mobilizing effect. For example, the combination of MIP-1xcex1 with G-CSF was found to increase white cell count in the blood as compared to G-CSF alone. Simm et al. Blood 1994, 84:2937. Co-administration of SCI with G-CSF caused the enhanced mobilization of a number of cell types including neutrophils, monocytes, eosinphils, lymphocytes and basophils. WO 94/28916. Administration of G-CSF alone had no effect on the release of eosinphils or basophils after 2 days of administration. Similar effects were observed when other agents such as GM-CSF, f-MET-Leu-Phe or IL-8 were coadministered with SCIs.
New chemokines have now been identified which also mobilize stem cells in an animal. These chemokines can be administered alone, or in combination with a colony stimulating factor or hemoregulatory agent to enhance mobilization of stem cells.
An object of the present invention is to provide novel chemokines for the mobilization of stem cells in an animal.
Another object of the invention is to provide a method of mobilizing stem cells.